The invention relates to a system for the storage and recovery of energy comprising a first storage space partly filled with a fluid, a second storage space, and a pump/turbine unit.
Various energy storage and recovery systems are widely known. In one known system the first storage space consists of a lake at a high location and the second storage space consists of a lake at a lower location or of an underground cavern, and there is a connecting line between the bottom part of the first storage space and the bottom part of the second storage space. Moreover, in such a system the pump/turbine unit is installed in the connecting line and located at the same height as or lower than the lower second storage space. Thus, during normal operation, the pump/turbine unit pumps a liquid from the second storage space to the higher, first storage space, and the turbine is driven by the liquid flowing back from the higher, first storage space to the lower, second storage space.
The pump of such a system is usually driven by an electric motor connected by an electric line to an electric network, and the turbine then drives an electric generator which is also connected by an electric line to an electric network. Such a system enables an excess of electrical energy to be used to pump the liquid to the higher, first storage space, while a storage of electrical energy can be supplemented by electrical energy generated by the electrical generator driven by the turbine, which is itself driven by liquid flowing back to the lower, second storage space. In the case of the second storage space being an underground cavern, it is necessary to make an additional separate space for the pump/turbine unit and to make a separate shaft through which to run an electric line of sufficient size to carry the electrical energy to the electric motor and from the electric generator since the pump/turbine unit is installed near the lower second storage space. This makes such a system extremely costly.